1. Field of the Invention
The present invention relates to an external skin patch, particularly to a hydrous external skin patch excellent in adherence and utility.
2. Description of the Related Art
In general, gel-like ointments, creams, liquids, patches, and the like are practically used as external skin preparations. Of those, the patches are effective preparations for treatment of affected areas which are usually covered with clothes (such as shoulder and back) because the patches can retain the effects of drugs for several hours per one-time use.
The patches may be broadly divided into non-aqueous adhesives and aqueous adhesives. Non-aqueous adhesives are plasters, plaster agents, and tapes which include a rubber adhesive, an acrylic (emulsion) adhesive, a silicon adhesive, or the like and do not substantially contain water. Aqueous adhesives are cataplasms which include a water-soluble acrylic adhesive and contain water at a relatively high level.
The non-aqueous adhesive has an advantage of high adherence, and high flexibility because of its small thickness of the paste (the total thickness of the support and the adhesive layer is 1 mm or less), for example. However, the non-aqueous adhesive has disadvantages of irritation to skin due to high occlusion degree of the preparation and peeling from skin particularly during sweating because the preparation includes a hydrophobic adhesive.
On the other hand, the aqueous adhesive has an advantage of low irritation to skin because the adhesive contains water at a high level. However, the aqueous adhesive has disadvantages of relatively low adherence, significantly lowered adherence due to evaporation of water, low flexibility because of the large thickness of the paste (the total thickness of the support and the adhesive layer is 1.5 mm or more), and dropping due to the weight of the preparation when the preparation absorbs an excessive amount of sweat, for example.
Moreover, there are also known novel hydrous patches containing both a non-aqueous adhesive and an aqueous adhesive (Patent Documents JP 06-145047 A and JP 06-145053 A). However, such novel hydrous patches also have insufficient adherence and contain a paste having low water absorbing ability, and hence tend to be easily peeled off particularly during sweating. In addition, the patches have a disadvantage that adhesion of the paste to itself before application to an affected area may make the patches unusable.
Although various studies have been made on enhancement of the adherence of patches (Patent Documents JP 05-139961 A, JP 06-219941 A, JP 08-295624 A, JP 11-302160 A, JP 08-175979 A and JP 2000-128780 A), all the methods are unsatisfactory because of insufficient adherence and complex production methods.